The present invention relates to an electrical switchgear and, more particularly, to venting a compartment of an arc-resistant enclosure for a switchgear.
Arc-resistant switchgear must withstand high internal pressure due to expanding gasses generated by an internal arc fault. For example, FIG. 1 shows the pressure rise due to an arc fault inside a breaker compartment (dark line). Thus, mechanisms are provided in the switchgear for internal pressure relief. Such mechanisms guard against structural damage to the switchgear cubicle by preventing the pressure rise beyond a safe value. One such mechanism is to have a large opening that connects a circuit breaker compartment or voltage transformer compartment to a vent chamber, with normally closed vent flaps. The flaps open to let the arc gasses out of the compartment and into the vent chamber. The peak internal pressure is determined by how soon the vent flaps open.
The structure of the flaps is related to the type of the switchgear construction as defined in the arc-resistant testing standard IEEE C37.20.7, namely, whether the switchgear is Type 2, Type 2B or Type 2C. Type 2C construction implies that no arc gasses will penetrate a compartment other than the one where the arc fault is created. This is a technically challenging requirement to meet. When the arc gasses flow through the vent chamber to an exhaust plenum, the reverse pressure can collapse the vent flaps into an adjacent breaker compartment. Hence the flaps are structurally reinforced and are heavy. This flap configuration, however, leads to a higher value of peak pressure before the vent flaps open to exhaust the arc gasses. For example, FIG. 2 shows effect of having a heavy vent flap that opens and releases the pressure inside of a breaker compartment. The peak pressure in the compartment is reduced from about 900 psi to 700 psi based on the vent flap opening when the pressure reaches about 112 psi.
Thus, there is a need to provide an improved vent flaps for a compartment of switchgear enclosure that are lightweight to provide quick opening, yet do not collapse under pressure from outside of the compartment.